Alarm warning system for swimming pools



June 21, 1960 c, c, ug u ETAL 2,942,247

ALARM WARNING FOR SWIMMING POOLS 2 Sheets-Sheet 1 Filed NOV. 6. 1956 Pl ll|| lllullllL ATTORNEYS.

c. c. LIENAU ETAL 2,942,247

ALARM WARNING FOR swmmmc POOLS z yl% June 21, 1960 2 Sheets-Sheet 2 Filed NOV. 6. 1956 d a/ A a e fwe 4 WM/ q p e 4 a w e a a r M a h 9 w a M 4 mm W m; 2 =2 m m w 2 9 w [M a w g m n y m A;

2,942,241 Patented-June 21, 1

ALARM WG SYSTEM FQR SING POULS Carl C. Lienau, 850 7th Ave., New York, N.Y-., and Joseph C. Patterson, J12, Falls Church, Va. (304 Albee Bldg., Washington 5, DC.)

Filed Nov. 6, 1956, Ser. No. 620,770

1 Claim. (Cl. 340-=258) This invention relates to apparatus for giving warning of an intruder such as a child entering an area surrounding a pool or falling into it, and a method of determining the specifications of the various units comprising the apparatus, to carry out this purpose. It is a continuation-in-part of our copending application Serial No. 381,324,v filed September '21, 1953 now Patent No. 2,783,459, granted February 26, 1957.

Residential swimming pools and to a lesser extent public pools are unsupervised or unattended, in the sense of direct observation by a competent person, during most of the day and night. During much of a twentyfour hour period a child may intrude upon the area immediately surrounding a pool or fall into the pool without being observed. This is evidenced in a tragic manner by the fact that during 1954, in the'city of Los Angeles alone there were over 20 drownings of children in pools comprised Within the 18,000 pools then in existence there. Over one-half of these took place behind conventional fences.

The number of swimming pools both public and private is rapidly multiplying all over the United States and some automatic alert means of giving warning of a child or other person falling into a pool or intruding within the-area surrounding a pool is land has long been urgently needed.

For convenience we use the term pool deck broadly to include not only the surface but the material under the surface of the area surrounding the pool, of a depth extending to at least below the level of the water in the pool.

The provision of an unseen signalling or alert fence as opposed to a passive barrier is the subject of this invention. The invention comprises theconception of selecting only impulses within a selected band of wave frequencies and of a predetermined minimum energy, which occur only once, such as the impulse occasioned by a child falling into the water a pool, and also a seriesof impulses within said band adding up to said energy within a selected period of time, such as a period of time sufiicient fora child to take three steps upon the surface of the area directly surrounding a pool, and excluding other energy impulses or tending to exclude all energy impulses such as would not by definition be called intruder signals. The invention also comprises apparatus including a vibration-sensitive receiver selectively responsive to pressure waves of different frequency to receive and translate into electrical energy impulses transmitted, through direct impact upon Water in.a pool, as in the case of a child falling into the pool, or through the material surrounding the pool, including cement, turf, earth, rock, gravel, etc., as is occasioned by the steps of a child upon the surface of the area directly surrounding thepool, and an electrical circuit system for exercising further selection and control to determine when the received energy will energize a warning signal. This system includes means for ampli-' fying the resulting electrical energy, means for filtering and attenuating the said energy to further restrict, it to within the selected frequency band, means for aggregating or integrating energy impulses within the selected 7 wave band received within a predetermined period, means for rectifying the energy from AC. to D.C., and means for creating a threshold (conditional transmission element) over which energy said band and ac cumulated within said period is passed to a warning signal device. .Such a threshold may be provided for example by a gas tube, such as the triode commercially available under thename Thyratron, which fires only above a characteristic threshold, or by a magnetic relay switch which in turn closes a circuit through a separate source. of power to a signalling device which is actuated by said separate source of power upon closing of said circuit.

In carrying out our invention we employ a vibration and/or pressure sensitive receiver for example a transducer positioned within the pool itself and preferably with its back against the side wall of the pool so that displacements of the sidewall inwardly of the poolsuch as are occasioned by the impact of the steps of a child upon the surface of the pool deck causes the transducer itself to be pushed'against the water in the pool thus causing a series of impacts upon the diaphragm of the transducer which are then translated in a well-known ay into electrical impulses. We cause these impulses to be transmitted successively to an amplifier, an electric wave filter and attenuator, a second amplifier, a conditional transmission element for adding impulses received within a given period of time, which we also refer to herein as an impulse adding rectifier? and an alarm device which once tripped continues to signal until it'is manually reset by a competent person thus called to the scene.

Walking or other actions of a child or other person on the pool deck or falling into the water, tend to produce characteristic frequencies of motion and pressure in t-hesolid, semi-solid and liquid materials involved;

These frequencies are selectively picked up by the transducer according to the range of frequencies of vibration for which it is constructed to respond, they are transmitted by the system in a way that may be expressed as an attenuation function of distance, frequency, and the nature of the medium through which the energy impulse is transmitted, i.e. the water and the pool deck.

To, exclude non-recurring impacts on the pool "deck, such for example as might be occasioned by a' chair blowing over we establish a minimum energy level such that the system will respond when a person takes a series of steps, say, for example, three steps, a given period, say three seconds. The minimum energy level to which the system will respond is therefore set at a level which will be exceeded by the sum of the impacts of three steps of a child on the pool deck. We have found that this energy level is below, the energy impact received by the transducer from even a very small child falling into the water in the pool, and so the minimum energy level for which the system is adjusted is such that the system will respond and a warning soundedas a result either of the single unit energy impact of a child falling into the pool or the multiple energy impact of a child taking three steps upon the pool deck.

The invention will best be understood if read in connection with the drawings in which: 4

Fig. l'is a schematic view.

Fig. 2 is a diagrammatic view of the electrical circuit means.

Fig. 3 is a detail view of the transducer means, in side elevation. Fig. 4 is a graph showing'firequency plotted against energy per unittime."

Fig. '5 is a graph showing time plotted in'relation to I energy received at transducer from impact of child falling into a pool, and I Fig. 6 is a graph showing energy accumulated ingthe systemfrom three footfalls plotted against a time interval. 7

It is desirableto rnake the system responsive to a narrow frequency band and onlyto impacts on the transdu in respect to which the voltage regulator 44 maintains the pointed at a constant potential, for example, 150 volts.

' noise level of microvolts; with the relay tripping input cer of more :th'an a predetermined .minimum 'hydro- I dynamic pressure intensity to exclude as completely as is practical all frequencies which may be transmitted tothe transducer from sources other than a'person'such as a within'a given time interval of a predetermined number of steps of an intruder on the pool 'deck. We have found that very satisfactory results are obtained using a frequen- 'cybandofiabout A0 ofone cycle per second toabout I fifty cycles per second, and aminimum hydrodynamic range of about 0.1 dyneto about 1 dyne per square centimeter. This arrangement precludes activating of lower frequencies such for example as the rumble of a truck.

7 child falling into the pool or; the accumulativeimpa'ct voltage at approximately 100 microvolts, and. with the voltage regulator Mwcontrolling thepower. supplied to point 46from source 12, at a level of approximately 150 ,volts with respect to the referencelevel (transducer housing, metal sheath 38, lead 40 and common lead or bus 42). Under these conditions the relay coil is normally I at a'voltage of approximately 60 volts and is held closed until the voltage falls to 6 volts when the relay circuit closes and the alarm is sounded. I I I Under these conditions the minimum operating level of r I the transducer ,is' approximately upwards of .02 of a.

pressure intensity on transducer diaphragm within a i I by energy sources other than a person falling into a pool or walking on the pool deck, using a frequency range of p Whilethe many factors involved are very ccmplex,we obtain very good results using the, system which we will.

now describe.

In the embodiment of the invention illustratedin .Figure 2 the, transducer ,lfi is positioned within a pool. and below the normal water levelwithin the pool, and connected to an alarm device, through anelectric circuit: which includes amplifier means, filter attenuator means, an impulse adding means, and a relay. The transducer as shown in Figure 3, comprises a housing 2,'the back "and sides of which may be made of bronze or similar metal, closed in front by a diaphragm 3 of stainless steel or similar anti corrosive material .01 thick. Within this 7 housing and attached to the diaphragm by suitable means such asadhesive is a piezo crystal or ceramic plate 5, 1" x /1" x .02", the opposite faces of which are plated with silver forming silver electrodes 6 and 7 from each of which lead wires 8 and 9 extend through the lead sheath 38 to the triode 11 of the system shown diagrammatically in Figure 1 and in detail in Figure 2.

Amplifier triode 11 comprises part of the amplifier filter attenuator means A F a. Anode 13 of triode 11 is connected to a source of voltage regulated power 12 through a decoupling filter circuit 14. Filter attenuator circuit F e connects triode 11 to triode 16, which is connected through filter-rectifier-integrating means F RI to the rectifier amplifier triode 20, the anode load circuit of which contains a relay coil 22, the contact 23 of which is normally closed and the contact 24 of which is normally open when the tube 20 is conducting. Contact 24 is connected to an alarm device 26 having its own source of energy 28. Switch 29 is an alarm inhibiting master switch provided to open the warning circuit as for example, manually when the pool is in intentional use by the owners -or authorized operators, or automatically, by known means, under other predictable conditions.

Contact 23 is part of a circuit comprising the grid biasing resistance ZS connected between: the grid and the cathode of tube 20. p

The reset switch 30 is provided for resetting the circuit after the relay has been tripped and an alarm sounded.

The system may include known means for giving warning if it is tampered with in any way, as for example, by cutting any of the electric leads or removing a fuse from the circuit, or by turning off the power source.

A metal sheath 38 surrounds the leads 8 and 9 from transducer 10 to triode 11, and the sheath. is grounded by a lead 40. Lead 42 which extends between the ground lead and the alarm device 26 is the electro mechanical reference level which is at zero voltage by definition and dyne per square centimeter hydrodynamic pressure ex erted on, the diaphragm of the transduce'n .Asstated above we have had good results, based on success in excluding actuation of the warning signal means from about 1/ 0 of 1 cycle per second, to about 50 cycles per second. However the totality of sonic and sub-sonic impulses madeby a person walking on a pooldeck or falling intoa pool is not a single frequencybut, awhole p spectrum of frequencies. -With properly proportioned 'filtering other portions of the spectrummay beemployed. I Under certain environmental noise such as a pool near aheavily travelled highway, the signal to noise ratio, and hence the discrimination of a, systeinfagainst road noises may be increased by using a'distributedsystem of; filtered transducers. While in the drawings'only one transducer is illustrated. it will be understood that several may be employed and included in the system. I I I i The operating power level of the system is a matter apart from the particular'frequency range, to which the warning system is made selective. It is determined by economic considerations, i.e. the current consumption andcost of the elements of the system. Different frequency ranges can be employed using the same operating level. For using different frequency ranges at a given operating level adjustment is made in the design of the transducer and in the filtering means.

Transistors can besubstituted for tubes 11, 16 and 20 and thus reduce the operating power level of the system and the size of the apparatus. At the present time however, I prefer to use the conventional tubes for reasons of economy and stability.

That part of the attenuation of distance source signals which is due to merely spatial dispersion of the energy falls of)"; with the distance. This fact helpsrto differentiate between local intruders and remotely generated disturbances due to transport machinerysuch as bumping of trucks on a nearby road. The dissipative attenuation of all disturbances traveling through the earth, concrete or water is distinct from and in addition to the foregoing spatial dispersion. Such energy dissipation as heat is dependent upon frequency. The dissipative transmission losses are a function of the frequency. It is exploited by usin the detection chain by proportiom'ng the filters so as to distinguish between disturbances of certain frequencies originatingnearby from disturbances of the same or other frequencies originating remotely. The effect of the frequency dependence of the dissipation is to introduce distance and therefore distance discrimination implicitly into the spectrum (K0); and transfer-factor of the chainrepresented by'tha't portion of the forgeese of the detecting chain is so designed as to provide a maximum of discrimination in favor of intrusions on the pool deck or in the pool.

Ordinary sounds in the air above the pool and pool deck are highly attenuated at the air-water interface and are generally above the band of frequencies which is optimum for the detection of intrusion as above defined. Sounds of wind, casual waves, shouting and airplanes are therefore ignored by the system. Water trickling sounds or rain sounds are similarly eliminated.

In order to help pre-establish the specifications or values for the units comprising the warning system which will cause the relay 22 to trip thus denoting transmission to the relay of energy within the selected frequency band and exceeding the minimum energy level, We have employed the formula:

=AL(At) volts Since we are concerned with an intruder such as a child or other person entering upon the pool deck or falling into the pool, we can in that formula consider that W is the weight of the child, h is the height through which the childs Weight falls yielding up a kinetic energy Wh by impact upon the receiving surface, which is either the pool deck or the water in the pool, d is the distance of the impact point from the transducer; K is a complex coeflicient determined pragmatically, i.e. by trial and error, and depending upon the source of the impact producing the vibrations and the medium of transmission known to those skilled in the art as spectral intensity; f is the frequency of the vibration and a is the area of the transducer diaphragm.

The symbols within the brackets represent the transfer chain by which the energy received from the transducer is modified by amplification, filtering, conversion from AC. to DC, and integrated for a predetermined time period before reaching the conditional transfer element, illustrated herein as a relay circuit. In the portion of the formula within the brackets the symbol S 0) stands for volts per dyne/cm. of pressure on the diaphragm of the transducer; A is a first step of amplification of the electrical voltage of selected frequency from the transducer and more exactly stands for voltage output per unit of voltage input of the first amplifier which is the triode 11 in Fig. 2; F 0) is a first filtering stage and more exactly stands for the voltage output per unit of voltage input of the filter portion of the amplifier-filterattenuator identified in Fig. 2 as A Foc in which a is the voltage output to voltage input ratio of the attenuator portion thereof; A is the second step of amplification, i.e. the voltage output to voltage input ratio of triode 16 comprising part of the amplifier-filter-rectifier-integrator circuit A F RI; F (f) is a second filtering step and more exactly represents the voltage output to voltage input ratio of the filter portion of A F RI; R stands for the means for rectifying or demodulating the output voltage of A 1 I stands for the storing and leaking action of the integrator; A (f) is a third step of amplification and represents the output to input voltage ratio of triode 20; and AL(At) is the DC. voltage output of the system at the relay coil 22 after a time interval At during which the impulses are being accumulated by the integrator I.

At the end of the detection chain there results a voltagev change AL(At) at the relay coil 22 referred to earth potential At seconds after the instant of impact, by definition taken as zero potential and as zero time respectively. The reference potential remains above earth potential by a constant amount. This potential difierence provides the necessary constant standard electrical threshold or 6 dividing line between alarm and no-alarm potentials, and is provided by a well-regulated supply voltage; one hundred and fifty volts is convenient when using triodes. With other means such as transistors a much lower voltage threshold may be used. The hydrodynamic pressure change Wit/ad is measured electrically at the diaphragmpiezo crystal or ceramic plate as a positive or negative departure from the long time average of the hydrostatic pressure.

By providing for adding or integrating impacts of a series of footsteps occurring in a time interval and employing the sum of these impacts to actuate a warning signal, we make it possible to give an alert to the danger of a child falling into a pool thus providing more time for averting a tragedy. By this means we provide a warning system which distinguishes the intrusion of a child or other person from the over-turning of a chair or the falling on the pool deck of a branch or limb the impact of which at the transducer is less than the established minimum energy level even if Within the selected frequency range, and also from a series of impacts each below said minimum level and occurring in a sequence pattern such that they do not add up to the minimum energy level within the established integrating time interval.

In practice a warning circuit made as disclosed herein for an average size pool can be used quite satisfactorily for both larger and smaller pools by simply adjusting the attenuating means. As on is increased the system responds to a signal of standard intensity and quality through a radius of increasing length from the transducer taken as center. between liability of the system to produce false alarms and the liability of missing a warning of a situation of the kind for which the system is intended.

There has thus been disclosed an apparatus in which the above-mentioned objects are embodied together with many practical advantages.

What we claim is:

An alarm circuit for producing an alarm in response to electrical waves amounting to more than a predetermined energy level within a predetermined integrating period of time which comprises, an input terminal to which said electrical waves are applied, an electronic tube of the vacuum type having a cathode, control grid and anode, a source of direct anode potential having positive and negative terminals, a lead from said positive terminal to the anode, a relay and a relay coil in said lead between said positive terminal and the anode, said relay comprising two contacts and a release arm movable between the two contacts, adapted to open at a predetermined coil current, one of said contacts being part of a circuit comprising a grid biasing resistance connected between the grid and said cathode, said contact being normally closed, and the other of said contacts being part of an alternate circuit interconnected between the negative terminal of the source of potential and said other contact and comprising an alarm means in series with its own source of power, and a lead connected between the negative terminal of said alarm source of power and the cathode through the normally closed contacts of said relay, said cathode being isolated from the negative terminal of said source of potential and said grid biasing resistance when the normally closed contact is open.

References Cited in the file of this patent UNITED STATES PATENTS 2,411,537 Goodale Nov. 26, 1946 2,435,996 Baird Feb. 17, 1948 2,513,279 Bradley July 4, 1950 2,655,645 Bagno Oct. 13, 1953 2,832,915 McCoy Apr. 29, 1958 The degree of sensitivity desired is a balance- 

